In order to perform realistic test runs on test benches for the testing of vehicles or vehicle components (test specimens), such as a vehicle, a drive train, an internal combustion engine, a transmission, a traction battery, etc., the tests have increasingly employed simulations of the vehicle, the test track, the vehicle environment, the interaction between vehicle and driving surface and the driver on the basis of suitable simulation models so that target values, such as speeds, torques, currents, voltages, etc. can be calculated for a test specimen on the test bench and for a load machine that is linked to it. This means that the test specimen is physically constructed on the test bench and is loaded by a load machine, e.g. by a torque or a speed. The vehicle, or a portion thereof, in which the test specimen is used is thereby simulated by simulation models, and the simulation supplements the physically constructed test specimen on the test bench for the test run. The term ‘test run’ is generally understood to mean loading the test specimen with a load variation with time via an interface, e.g. in the form of a torque-time diagram or torque-speed diagram. The objective of this is, for instance, to drive over a test route with the test specimen, wherein the test specimen is arranged on the test bench—the test specimen is thus intended to experience the same load as if the test specimen were really driving on the test route in a real vehicle.
When using simulation models for the test run, the target values for the test run are calculated from the simulation models at usually constant intervals, e.g. at a frequency of 1 kHz, in real time and are adjusted on the test bench by the test specimen and the load machine. Additionally, particular measurement values, such as torques and speeds, are detected by measurement on the test bench and processed in the simulation. However, for more highly dynamic control processes, such as braking maneuvers or quick acceleration, shorter intervals of time are desirable and necessary for realistic test runs. Nevertheless, limits are reached very quickly because of the available computing capacity, since the target values cannot be calculated fast enough. Cycle times of up to 10 kHz or more are required for the control process to create highly dynamic, realistic applications, which is currently not economically feasible with sufficient precision. One must either simplify the simulation model in order to get by with the available computing capacity or be satisfied with large time intervals in the control process. In practice, however, both of these options are not satisfactory for highly dynamic processes.
In particular, realistically taking into account the behavior between the tires and the driving surface, e.g. tire slippage, places high demands on the simulation. In this regard, EP 1 037 030 B1 discloses a method that permits the behavior of the vehicle on a driving surface to be simulated as realistically as possible. In so doing, the slipping behavior of the tire is calculated based on a tire model in a simulation unit. The tire model provides a torque, which is given as a target value to the load machine simulating the tire on the test bench and which is adjusted on the test bench, and a longitudinal force, which is transferred from the tire to the driving surface and which is processed in a vehicle model to calculate the vehicle velocity. The tire behavior is thus simulated entirely on a simulator computer. The possible dynamics are determined by the capacity of the simulation computer and/or by the complexity of the simulation model. Control cycle times of 1-3 kHz are typically possible using this method, but this is insufficient for realistic, highly dynamic test runs.
Maintaining a tire model such as the one in EP 1 037 030 B1 is relatively laborious, though, since the entire tire model can become highly complex. Apart from this, modifying or adapting the tire model, even a part of it, is also difficult for the same reasons. Not least of all, the tire model is also inflexible, since the implemented model is firmly established. If one wishes to use a different tire model or another part of the tire model, e.g. to calculate the transverse force or tire slippage, the entire tire model must be exchanged or adapted.
Therefore, the problem addressed by the present invention is that of making the handling of a tire model for controlling a test run on a test bench simpler and more flexible and thus more practicable.